Abstract: :
Purpose: Frequency-doubling technology (FDT) can reportedlydiagnose early glaucomatous changes through detecting damagein magnocellular projecting retinal ganglion cells (M cells),which are more liable to pressure-induced damage. In eyes withopen-angle glaucoma(OAG) with visual field defects confinedto either lower or upper hemifield, early glaucomatous damageis also likely in the half optic disc corresponding to the sparedhemifield. This study aims to study difference in M cell damagebetween OAG with elevated pressure (primary open angle glaucoma:POAG)and that with normal pressure(normal tension glaucoma:NTG) byFDT outcomes obtained from the spared hemifield.Method: Fifty-eighteyes of 58 early-stage OAG patients with elevated pressure (POAG)patients and 68 eyes of 68 early-stage OAG patients with normalpressure (NTG) with visual field defects as detected by HFA30-2 program confined to either lower or upper hemifield wereincluded. In FDT testing, patients were first tested with C-20screening program, then with N-30 threshold program in eachregularly visit. Data of the second results obtained with N-30program were used. FDT-measured thresholds of each test pointand its averages (FDT hemifield mean) over the hemifield judgedto be normal or abnormal by HFA were compared between the POAGand the NTG groups.Results: Age, refraction (spherical equivalent),and mean deviation (MD) measured by HFA showed no significantof inter-group difference (55.6 ± 10.2 vs 58.6 ±9.3 years, -3.2 ± 2.8 vs -2.4 ± 3.4 D, and -3.9±3.2 vs -4.1 ± 3.3 dB, respectively), while thehighest intraocular pressure(IOP) recorded was 24.9 ±4.4 mmHg in the POAG and 17.6 ± 1.9 mmHg in the NTG group,(p<0.001;Wilcoxon rank sum test). Mean of TD values in eitherdamaged or spared hemifield showed no significant inter-groupdifference. In the hemifield judged to be normal by HFA, FDT-measuredthresholds at 8 of 9 points and FDT hemifield mean (27.5 ±2.8 vs. 24.4 ± 3.2 dB; p < 0.001) were significantlyhigher in the NTG than in the POAG group. In the abnormal hemifield,FDT-measured thresholds at all points and FDT hemifield meanshowed no significant inter-group difference.Conclusion: Thepresent result suggest difference in contribution of IOP-dependentdamage between the two types of OAG and that FDT can sensitivelydetect IOP dependent damage, being more useful for early detectionof glaucoma with elevated IOP.